Berlin 2018 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 57: Methods in Computational Materials Modelling (methodological aspects, numerics)

MM 57.5: Talk

Thursday, March 15, 2018, 12:45–13:00, TC 006

Full Configuration Interaction Quantum Monte Carlo study of the spin polarized three dimensional uniform electron gas — •Michele Ruggeri¹, Pablo Lopez Rios^1,2, and Ali Alavi^1,3 — ¹Max Planck Institute for Solid State Research, Heisenbergstr. 1, 70569 Stuttgart, Germany — ²Theory of Condensed Matter Group, Cavendish Laboratory, J. J. Thomson Avenue, Cambridge CB3 0HE, UK — ³University Chemical Laboratory, Lensfield Road, Cambridge, CB2 1EW, UK

The uniform electron gas is system consisting in electrons in a uniform positive background, which can be used to model electrons in a metal and to study electronic correlations. Quantum Monte Carlo methods, especially DMC with the fixed node approximation, proved to be a powerful tool to study the uniform electron gas, but due to the sign problem these QMC results are only variational. It is however possible to obtain essentially exact estimates of the energy of electronic systems using Full Configuration Interaction Quantum Monte Carlo (fciqmc).

We compare fixed node DMC and fciqmc energies for the three dimensional spin polarized uniform electron gas in the high density regime (r_S = 0.5 and 1.0) for different system sizes (N = 7 to 33 electrons), giving an estimate of the fixed node error. We show that it is possible to improve the fixed node energies using multi-determinant trial wave functions, obtaining results in agreement with fciqmc if a large enough number of determinants is used. Twist averaged boundary conditions are in use to reduce finite size effects.